A camshaft for use in an internal combustion engine of a type having spring loaded cam followers experiences a series of oppositely directed torque pulses during each revolution of the camshaft. The positive-going portion of each pulse occurs as a result of the need to apply torque to the camshaft to cause each of its operating cams to rotate against the force of the cam follower during the opening of the valve which is operated by such cam follower, and the negative-going portion occurs as the result of the application of an oppositely directed torque to the camshaft as the operating cam resists the force of the cam follower during the closing of the valve.
The resulting torque pulses can be used for actuation purposes, e.g., as a means for providing a control signal to a variable cam timing system (VCT) as disclosed in U.S. Pat. No. 5,002,023. The present invention incorporates by reference the disclosure of said U.S. patent.
For certain applications (usually inline 4-cylinder and 6-cylinder engines), however, the torque pulses may not be of sufficient magnitude for actuation of a VCT system according to U.S. Pat. No. 5,002,023. In these cases the torque pulses must be amplified to be utilized effectively.
The use of an additional cam lobe added to the length of the cam shaft is known.
U.S. Pat. No. 5,107,805 discloses a torque amplifying camshaft for operating a valve of each of a plurality valves of an internal combustion engine, the camshaft having an elongagted, shaftlike portion and an engine valve operating cam for each of the valves, the valve operating cams being spaced apart from one another along the shaftlike portion. Each of the engine valve operating cams has an outwardly projecting portion, and the outwardly projecting portions are circumferentially offset from one another about the longitudinal central axis of the camshaft. The camshaft also carries a supplementary cam surface, either in the form of an outwardly facing surface of a separate supplementary cam or an inwardly facing surface of a portion of a drive sprocket which is keyed to the shaftlike portion. The supplementary cam surface is adapted to be followed by a spring biased supplementary cam follower and has portions which introduce torque pulses into the camshaft which are synchronous with and consistently directed with respect to the torque pulses that are introduced into the camshaft by the engagement between the valve operating cams and spring biased followers which engage such valve operating cams.
U.S. Pat. No. 5,040,500 discloses a torque compensated camshaft for operating a valve of each of a plurality of valves of an internal combustion engine, the camshaft having an elongate shaftlike portion and an engine valve operating cam for each of the valves, the valve operating cams being spaced apart from one another along the shaftlike portion. Each of the engine valve operating cams has an outwardly projecting portion, and the outwardly projecting portions are circumferentially offset from one another about the longitudinal central axis of the camshaft. The camshaft also carries a compensating cam surface, either in the form of an outwardly facing surface of a separate compensating cam or an inwardly facing surface of a portion of a drive sprocket which is keyed to the shaftlike portion. The compensating cam surface is adapted to be followed by a spring biased compensating cam follower and has portions which introduce torque pulses into the camshaft which are synchronous with and oppositely directed with respect to the torque pulses that are introduced into the camshaft by the engagement between the valve operating cams and spring biased followers which engage such valve operating cams.
However, some additional cam lobe takes significant space such as extra length of a cam shaft. Many engines do not have the space for accommodating this type extra lobe in the engine compartment. Therefore, it is desirable to provide extra lobes that do not occupy excessive space in which the accommodating extra lobes are located.